From f230bb86398d7e05d179d6c9fce7a4fbe83b0b69 Mon Sep 17 00:00:00 2001
From: Eugene Leviant <eleviant@accesssoftek.com>
Date: Fri, 5 Jul 2019 12:10:44 +0000
Subject: [PATCH] [llvm-objcopy] Allow strip symtab from executables and DSOs

Differential revision: https://reviews.llvm.org/D61672


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365193 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../ELF/no-symbol-relocation.test             |  2 +-
 .../preserve-segment-contents-ehdr-phdrs.test |  2 +-
 .../ELF/remove-multiple-sections.test         | 28 -----------------
 .../ELF/segment-shift-section-remove.test     | 30 +------------------
 .../ELF/segment-test-remove-section.test      | 30 +------------------
 .../ELF/strip-unneeded-all-symbols.test       | 21 +++++++++++++
 tools/llvm-objcopy/ELF/ELFObjcopy.cpp         |  2 +-
 tools/llvm-objcopy/ELF/Object.cpp             | 21 +++++++++++++
 tools/llvm-objcopy/ELF/Object.h               |  3 ++
 9 files changed, 50 insertions(+), 89 deletions(-)
 create mode 100644 test/tools/llvm-objcopy/ELF/strip-unneeded-all-symbols.test

diff --git a/test/tools/llvm-objcopy/ELF/no-symbol-relocation.test b/test/tools/llvm-objcopy/ELF/no-symbol-relocation.test
index 9def536c239..64d36631856 100644
--- a/test/tools/llvm-objcopy/ELF/no-symbol-relocation.test
+++ b/test/tools/llvm-objcopy/ELF/no-symbol-relocation.test
@@ -6,7 +6,7 @@
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
-  Type:            ET_EXEC
+  Type:            ET_REL
   Machine:         EM_X86_64
 Sections:
   - Name:            .text
diff --git a/test/tools/llvm-objcopy/ELF/preserve-segment-contents-ehdr-phdrs.test b/test/tools/llvm-objcopy/ELF/preserve-segment-contents-ehdr-phdrs.test
index 9dc63d753f6..3352313c271 100644
--- a/test/tools/llvm-objcopy/ELF/preserve-segment-contents-ehdr-phdrs.test
+++ b/test/tools/llvm-objcopy/ELF/preserve-segment-contents-ehdr-phdrs.test
@@ -13,7 +13,7 @@
 # BEFORE:      Type: PT_LOAD
 # BEFORE-NEXT: Offset: 0x240
 
-# AFTER:      SectionHeaderCount: 5
+# AFTER:      SectionHeaderCount: 3
 # AFTER:      Type: PT_LOAD
 # AFTER-NEXT: Offset: 0x0
 # AFTER:      Type: PT_LOAD
diff --git a/test/tools/llvm-objcopy/ELF/remove-multiple-sections.test b/test/tools/llvm-objcopy/ELF/remove-multiple-sections.test
index 1f1bc4ce191..a162303ccac 100644
--- a/test/tools/llvm-objcopy/ELF/remove-multiple-sections.test
+++ b/test/tools/llvm-objcopy/ELF/remove-multiple-sections.test
@@ -87,34 +87,6 @@ Sections:
 # CHECK:   }
 # CHECK:   Section {
 # CHECK:     Index: 4
-# CHECK:     Name: .symtab
-# CHECK:     Type: SHT_SYMTAB (0x2)
-# CHECK:     Flags [ (0x0)
-# CHECK:     ]
-# CHECK:     Address: 0x0
-# CHECK:     Offset:
-# CHECK:     Size:
-# CHECK:     Link: 5
-# CHECK:     Info: 1
-# CHECK:     AddressAlignment: 8
-# CHECK:     EntrySize: 24
-# CHECK:   }
-# CHECK:   Section {
-# CHECK:     Index: 5
-# CHECK:     Name: .strtab
-# CHECK:     Type: SHT_STRTAB (0x3)
-# CHECK:     Flags [ (0x0)
-# CHECK:     ]
-# CHECK:     Address: 0x0
-# CHECK:     Offset:
-# CHECK:     Size:
-# CHECK:     Link: 0
-# CHECK:     Info: 0
-# CHECK:     AddressAlignment: 1
-# CHECK:     EntrySize: 0
-# CHECK:   }
-# CHECK:   Section {
-# CHECK:     Index: 6
 # CHECK:     Name: .shstrtab
 # CHECK:     Type: SHT_STRTAB (0x3)
 # CHECK:     Flags [ (0x0)
diff --git a/test/tools/llvm-objcopy/ELF/segment-shift-section-remove.test b/test/tools/llvm-objcopy/ELF/segment-shift-section-remove.test
index 563a9e3f836..cef783cb9b2 100644
--- a/test/tools/llvm-objcopy/ELF/segment-shift-section-remove.test
+++ b/test/tools/llvm-objcopy/ELF/segment-shift-section-remove.test
@@ -41,7 +41,7 @@ ProgramHeaders:
     Sections:
       - Section: .text3
 
-#CHECK: SectionHeaderCount: 6
+#CHECK: SectionHeaderCount: 4
 
 # CHECK:           Sections [
 # CHECK-NEXT:        Section {
@@ -92,34 +92,6 @@ ProgramHeaders:
 # CHECK-NEXT:        }
 # CHECK-NEXT:        Section {
 # CHECK-NEXT:          Index: 3
-# CHECK-NEXT:          Name: .symtab
-# CHECK-NEXT:          Type: SHT_SYMTAB (0x2)
-# CHECK-NEXT:          Flags [ (0x0)
-# CHECK-NEXT:          ]
-# CHECK-NEXT:          Address: 0x0
-# CHECK-NEXT:          Offset: 0x3000
-# CHECK-NEXT:          Size: 24
-# CHECK-NEXT:          Link: 4
-# CHECK-NEXT:          Info: 1
-# CHECK-NEXT:          AddressAlignment: 8
-# CHECK-NEXT:          EntrySize: 24
-# CHECK-NEXT:        }
-# CHECK-NEXT:        Section {
-# CHECK-NEXT:          Index: 4
-# CHECK-NEXT:          Name: .strtab
-# CHECK-NEXT:          Type: SHT_STRTAB (0x3)
-# CHECK-NEXT:          Flags [ (0x0)
-# CHECK-NEXT:          ]
-# CHECK-NEXT:          Address: 0x0
-# CHECK-NEXT:          Offset: 0x3018
-# CHECK-NEXT:          Size:
-# CHECK-NEXT:          Link: 0
-# CHECK-NEXT:          Info: 0
-# CHECK-NEXT:          AddressAlignment: 1
-# CHECK-NEXT:          EntrySize: 0
-# CHECK-NEXT:        }
-# CHECK-NEXT:        Section {
-# CHECK-NEXT:          Index: 5
 # CHECK-NEXT:          Name: .shstrtab
 # CHECK-NEXT:          Type: SHT_STRTAB (0x3)
 # CHECK-NEXT:          Flags [ (0x0)
diff --git a/test/tools/llvm-objcopy/ELF/segment-test-remove-section.test b/test/tools/llvm-objcopy/ELF/segment-test-remove-section.test
index f9a5dd7811e..60cd5f3483d 100644
--- a/test/tools/llvm-objcopy/ELF/segment-test-remove-section.test
+++ b/test/tools/llvm-objcopy/ELF/segment-test-remove-section.test
@@ -46,7 +46,7 @@ ProgramHeaders:
 # Make sure that when we remove a section we overwrite it with zeros
 # DATA: {{^[^[:blank:]]+}} 00 00 00 00
 
-#CHECK: SectionHeaderCount: 6
+#CHECK: SectionHeaderCount: 4
 
 # CHECK: Sections [
 # CHECK:   Section {
@@ -97,34 +97,6 @@ ProgramHeaders:
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 3
-# CHECK-NEXT:     Name: .symtab
-# CHECK-NEXT:     Type: SHT_SYMTAB (0x2)
-# CHECK-NEXT:     Flags [ (0x0)
-# CHECK-NEXT:     ]
-# CHECK-NEXT:     Address: 0x0
-# CHECK-NEXT:     Offset:
-# CHECK-NEXT:     Size:
-# CHECK-NEXT:     Link: 4
-# CHECK-NEXT:     Info: 1
-# CHECK-NEXT:     AddressAlignment: 8
-# CHECK-NEXT:     EntrySize: 24
-# CHECK-NEXT:   }
-# CHECK-NEXT:   Section {
-# CHECK-NEXT:     Index: 4
-# CHECK-NEXT:     Name: .strtab
-# CHECK-NEXT:     Type: SHT_STRTAB (0x3)
-# CHECK-NEXT:     Flags [ (0x0)
-# CHECK-NEXT:     ]
-# CHECK-NEXT:     Address: 0x0
-# CHECK-NEXT:     Offset:
-# CHECK-NEXT:     Size:
-# CHECK-NEXT:     Link: 0
-# CHECK-NEXT:     Info: 0
-# CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
-# CHECK-NEXT:   }
-# CHECK-NEXT:   Section {
-# CHECK-NEXT:     Index: 5
 # CHECK-NEXT:     Name: .shstrtab
 # CHECK-NEXT:     Type: SHT_STRTAB (0x3)
 # CHECK-NEXT:     Flags [ (0x0)
diff --git a/test/tools/llvm-objcopy/ELF/strip-unneeded-all-symbols.test b/test/tools/llvm-objcopy/ELF/strip-unneeded-all-symbols.test
new file mode 100644
index 00000000000..e2fd4202115
--- /dev/null
+++ b/test/tools/llvm-objcopy/ELF/strip-unneeded-all-symbols.test
@@ -0,0 +1,21 @@
+## Stripping unneeded symbols from execuatble/DSO should
+## eliminate the static symbol table, because it's not used
+## by the dynamic loader. 
+
+# RUN: yaml2obj %s > %t
+# RUN: cp %t %t1
+# RUN: llvm-objcopy --strip-unneeded %t %t2
+# RUN: llvm-readobj --section-headers %t2 | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:    ELFCLASS64
+  Data:     ELFDATA2LSB
+  Type:     ET_EXEC
+  Machine:  EM_X86_64
+Symbols:
+  - Name:     bar
+  - Name:     foo
+    Binding:  STB_GLOBAL
+
+# CHECK-NOT: .symtab
diff --git a/tools/llvm-objcopy/ELF/ELFObjcopy.cpp b/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
index b366c6e5598..bbaac96f070 100644
--- a/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ b/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -423,7 +423,7 @@ static Error updateAndRemoveSymbols(const CopyConfig &Config, Object &Obj) {
 
     if ((Config.StripUnneeded ||
          is_contained(Config.UnneededSymbolsToRemove, Sym.Name)) &&
-        isUnneededSymbol(Sym))
+        (!Obj.isRelocatable() || isUnneededSymbol(Sym)))
       return true;
 
     // We want to remove undefined symbols if all references have been stripped.
diff --git a/tools/llvm-objcopy/ELF/Object.cpp b/tools/llvm-objcopy/ELF/Object.cpp
index fa696380e17..2d85b3ad36f 100644
--- a/tools/llvm-objcopy/ELF/Object.cpp
+++ b/tools/llvm-objcopy/ELF/Object.cpp
@@ -1995,6 +1995,25 @@ template <class ELFT> Error ELFWriter<ELFT>::write() {
   return Buf.commit();
 }
 
+static Error removeUnneededSections(Object &Obj) {
+  // We can remove an empty symbol table from non-relocatable objects.
+  // Relocatable objects typically have relocation sections whose
+  // sh_link field points to .symtab, so we can't remove .symtab
+  // even if it is empty.
+  if (Obj.isRelocatable() || Obj.SymbolTable == nullptr ||
+      !Obj.SymbolTable->empty())
+    return Error::success();
+
+  // .strtab can be used for section names. In such a case we shouldn't
+  // remove it.
+  auto *StrTab = Obj.SymbolTable->getStrTab() == Obj.SectionNames
+                     ? nullptr
+                     : Obj.SymbolTable->getStrTab();
+  return Obj.removeSections(false, [&](const SectionBase &Sec) {
+    return &Sec == Obj.SymbolTable || &Sec == StrTab;
+  });
+}
+
 template <class ELFT> Error ELFWriter<ELFT>::finalize() {
   // It could happen that SectionNames has been removed and yet the user wants
   // a section header table output. We need to throw an error if a user tries
@@ -2004,6 +2023,8 @@ template <class ELFT> Error ELFWriter<ELFT>::finalize() {
                              "cannot write section header table because "
                              "section header string table was removed");
 
+  if (Error E = removeUnneededSections(Obj))
+    return E;
   Obj.sortSections();
 
   // We need to assign indexes before we perform layout because we need to know
diff --git a/tools/llvm-objcopy/ELF/Object.h b/tools/llvm-objcopy/ELF/Object.h
index f3df93b9662..e56c155cfef 100644
--- a/tools/llvm-objcopy/ELF/Object.h
+++ b/tools/llvm-objcopy/ELF/Object.h
@@ -1051,6 +1051,9 @@ public:
     Segments.emplace_back(llvm::make_unique<Segment>(Data));
     return *Segments.back();
   }
+  bool isRelocatable() const {
+    return Type != ELF::ET_DYN && Type != ELF::ET_EXEC;
+  }
 };
 
 } // end namespace elf
-- 
2.40.0